Active magnetic regenerative liquefier using process gas pre-cooling from bypass flow of heat transfer fluid

ABSTRACT

A process for liquefying hydrogen gas into liquid hydrogen that includes:
         continuously introducing hydrogen gas into an active magnetic regenerative refrigerator module, wherein the module has one, two, three or four stages, wherein each stage includes a bypass flow heat exchanger that receives a bypass helium heat transfer gas from a cold side of a low magnetic or demagnetized field section that includes a magnetic refrigerant bed at a hydrogen gas first cold inlet temperature and discharges hydrogen gas or fluid at a first cold exit temperature; wherein sensible heat of the hydrogen gas is entirely removed by the bypass flow heat exchanger in the one stage module or a combination of the bypass flow heat exchangers in the two, three or four stage module, the magnetic refrigerant bed operates at or below its Curie temperature throughout an entire active magnetic regeneration cycle, and a temperature difference between the bypass helium heat transfer first cold inlet temperature and the hydrogen gas first cold exit temperature is 1 to 2 K for each bypass flow heat exchanger.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.15/438,529, filed Feb. 21, 2017, which claims the benefit of U.S.Provisional Application No. 62/298,346, filed Feb. 22, 2016, which isincorporated herein by reference in its entirety.

ACKNOWLEDGEMENT OF GOVERNMENT SUPPORT

This invention was made with government support under Contract No.DE-AC05-76RL01830 awarded by the U.S. Department of Energy. Thegovernment has certain rights in the invention.

BACKGROUND

Broad use of hydrogen as a fuel or energy carrier will provide betterenergy security, return major economic, environmental, and healthbenefits, and help minimize climate-change impact of greenhouse-gasemissions from energy use. Hydrogen couples into any realistic model of“sustainable carbon-hydrogen-electricity cycles” in an integrated andcritical manner.

For storage and delivery, liquid hydrogen (LH₂) is the superior choicerather than compressed (CH₂), adsorbed, or chemical compounds ofhydrogen because of LH₂'s higher volumetric energy density andgravimetric energy density compared to other hydrogen storage methods.The ratio of the ideal minimum work input per unit mass of gas to thereal work input per unit mass of gas for a practical liquefier is calledfigure of merit (FOM). Currently the majority of gaseous hydrogen (GH₂)is liquefied using liquid nitrogen pre-cooled Claude-cycle plants. Theseconventional large-scale liquefiers are limited to a FOM of ˜0.35.Small-scale conventional liquefiers seldom achieve FOMs of 0.25. Such alow FOM increases operating costs of hydrogen liquefiers and thereby theprice of dispensed LH₂ or CH₂ fuel.

A relatively small number of hydrogen liquefiers presently exist in theworld. Most of them are large industrial plants with capacities rangingfrom ˜5 metric tons/day to ˜100 metric tons/day. The majority ofcommercial H₂ has been used for non-transportation applications such asat refineries and ammonia fertilizer plants. Few commercial liquefactionfacilities have been built with capacities below ˜5 metric tons/daybecause the installed costs tend to increase sharply on a per metricton/day basis as the capacity decreases. The depreciation of highcapital costs of hydrogen liquefiers increases the price of dispensedLH₂ or CH₂ fuel. For example, a 1 metric ton/day LH₂ facility has anapproximate installed cost of ˜$9-11 million, i.e., ˜$10 million/metricton/day. Over a 20-year operating period of a plant of this capacity andcost, straight-line depreciation gives a contribution of ˜$1.45/kg H₂ tofuel cost.

The major barriers to deployment of fuel-cell electric vehicles are lackof local supply and refueling infrastructure with capacity in the rangeof 0.1 to 1 metric ton/day at each refueling station with delivery ofLH₂ or CH₂ at the same price or less than gasoline on a fuel cost/miledriven basis. Cost-effective and efficient hydrogen liquefiers on thisscale for such refueling supply and refueling stations do not exist.

These two key barriers to rapid adoption of hydrogen fuels can beeliminated by development of highly-efficient and low-cost small-scaleliquefiers.

SUMMARY

One embodiment disclosed herein is a process for liquefying a processgas comprising:

introducing a heat transfer fluid into an active magnetic regenerativerefrigerator apparatus that comprises (i) a high magnetic field sectionin which the heat transfer fluid flows from a cold side to a hot sidethrough at least one magnetized bed of at least one magneticrefrigerant, (ii) a first no heat transfer fluid flow section in whichthe bed is demagnetized, (iii) a low magnetic or demagnetized fieldsection in which the heat transfer fluid flows from a hot side to a coldside through the demagnetized bed, and (iv) a second no heat transferfluid flow section in which the bed is magnetized; continuouslydiverting a bypass portion of the heat transfer fluid from the cold sideof the low magnetic or demagnetized field section into a bypass flowheat exchanger at a first cold inlet temperature; and

continuously introducing the process gas into the bypass flow heatexchanger at a first hot inlet temperature and discharging the processgas or liquid from the bypass flow heat exchanger at a first cold exittemperature;

wherein the temperature difference between the bypass heat transferfirst cold inlet temperature and the process gas first cold exittemperature is 1 to 5 K.

Also disclosed herein is a process for liquefying a process gascomprising:

introducing a heat transfer fluid into an active magnetic regenerativerefrigerator apparatus that comprises (i) a high magnetic field sectionin which the heat transfer fluid flows from a cold side to a hot sidethrough at least one magnetized bed of at least one magneticrefrigerant, (ii) a first no heat transfer fluid flow section in whichthe bed is demagnetized, (iii) a low magnetic or demagnetized fieldsection in which the heat transfer fluid flows from a hot side to a coldside through the demagnetized bed, and (iv) a second no heat transferfluid flow section in which the bed is magnetized;

continuously diverting a bypass portion of the heat transfer fluid fromthe cold side of the low magnetic or demagnetized field section into abypass flow heat exchanger at a first cold inlet temperature; and

continuously introducing the process gas into the bypass flow heatexchanger at a first hot inlet temperature and discharging the processgas or liquid from the bypass flow heat exchanger at a first cold exittemperature;

wherein the magnetic refrigerant operates at or below its Curietemperature throughout an entire active magnetic regeneration cycle.

Further disclosed herein is a process for liquefying a process gascomprising:

introducing a heat transfer fluid into an active magnetic regenerativerefrigerator apparatus that comprises (i) a high magnetic field sectionin which the heat transfer fluid flows from a cold side to a hot sidethrough at least one magnetized bed of at least one magneticrefrigerant, (ii) a first no heat transfer fluid flow section in whichthe bed is demagnetized, (iii) a low magnetic or demagnetized fieldsection in which the heat transfer fluid flows from a hot side to a coldside through the demagnetized bed, and (iv) a second no heat transferfluid flow section in which the bed is magnetized; continuouslydiverting a bypass portion of the heat transfer fluid from the cold sideof the low magnetic or demagnetized field section into a bypass flowheat exchanger at a first cold inlet temperature; and

continuously introducing the process gas into the bypass flow heatexchanger at a first hot inlet temperature and discharging the processgas or liquid from the bypass flow heat exchanger at a first cold exittemperature;

wherein the sensible heat of the process gas is entirely removed by thebypass flow heat exchanger.

Additionally disclosed herein is a process for liquefying hydrogen gasinto liquid hydrogen comprising:

continuously introducing hydrogen gas into an active magneticregenerative refrigerator module, wherein the module has one to fourstages, wherein each stage includes a bypass flow heat exchanger thatreceives a bypass helium heat transfer gas from a cold side of a lowmagnetic or demagnetized field magnetic refrigerant bed at a first coldinlet temperature and discharges hydrogen gas or fluid at a first coldexit temperature; wherein the sensible heat of the hydrogen gas isentirely removed by the bypass flow heat exchanger, the magneticrefrigerant operates at or below its Curie temperature throughout anentire active magnetic regeneration cycle, and the temperaturedifference between bypass helium heat transfer first cold inlettemperature and the hydrogen gas first cold exit temperature is 1 to 2K.

Further disclosed herein is a system comprising:

an active magnetic regenerative refrigerator apparatus that comprises(i) a high magnetic field section in which a heat transfer fluid canflow from a cold side to a hot side through at least one magnetized bedof at least one magnetic refrigerant, (ii) a first no heat transferfluid flow section in which the bed can be demagnetized, (iii) a lowmagnetic or demagnetized field section in which the heat transfer fluidcan flow from a hot side to a cold side through the demagnetized bed,and (iv) a second no heat transfer fluid flow section in which the bedcan be magnetized; and

a single bypass flow heat exchanger (a) fluidly coupled to the cold sideof the low magnetic or demagnetized field section and (b) fluidlycoupled to a process gas source, wherein the single bypass flow heatexchanger can remove all of the sensible heat of the process gas.

This will become more apparent from the following detailed description,which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a cross-section of a rotary wheelembodiment of a single-stage active magnetic regenerative refrigerator(AMRR) with bypass flow. For example, the embodiment shown in FIG. 1 isa schematic diagram of a single stage AMRR with layered magneticmaterials and bypass flow of heat transfer fluid to continuously cool aprocess stream such as gaseous H₂ (GH2) or natural gas. In this stagethere are eight magnetic materials to span from ˜280 K to ˜122 K. Thisdesign also works for 122 K to 53 K or from 53 K to 22 K; each withfewer layers of refrigerants and less material as required for a LH₂liquefier.

FIG. 2 is a schematic of 3 AMRR-stages with continuous bypass flow in aseries configuration as a H₂ liquefier.

FIG. 3 is a block process flow diagram of a gaseous H₂ (GH2) to liquidH₂ (LH₂) liquefier facility with multistage AMRRs with bypass flow.

FIG. 4 is a schematic diagram of a helium gas heat transfer sub-systemwith continuous bypass flow in two sets of reciprocating layeredmagnetic regenerators with superconducting magnets in an active magneticregenerator cycle.

DETAILED DESCRIPTION

Disclosed herein are processes and systems that include active magneticregenerative refrigerators (AMRRs) for liquefying process gases such as,for example, hydrogen, natural gas, helium, propane, and other gases orgas mixtures. The AMRR processes and systems can have severalconfigurations such as reciprocating dual active magnetic regeneratorsor continuously rotating active magnetic regenerators with one or morelayers of magnetic refrigerants that execute active magneticregenerative cycles when coupled to a reversing flow of heat transfergas or liquid in the magnetized or demagnetized stage of the cycle. Foroptimal heat transfer, different mass flow rates of heat transfer gasare required in these two stages (i.e., magnetized vs. demagnetized),and this is accomplished by bypass of some cold heat transfer gas fromthe hot-to-cold flow stage before the cold-to-hot flow stage of thecycle. For example, maximum use of continuous flow of cold sensible heatin the bypass stream as it returns to higher temperatures in acounterflow heat exchanger to continuously cool a process gas stream canincrease the FOM of an active magnetic regenerative liquefier (AMRL)from ˜0.35 in conventional gas-cycle liquefiers to ˜0.60 or more inAMRLs. Besides increasing the FOM, the use of bypass stream tocontinuously and completely cool the process gas significantly reducesthe refrigeration capacity per AMRR stage and thereby reduces the massof magnetic refrigerants required in the AMRL. Rotary AMRLsintrinsically have continuous bypass gas flow for continuous pre-coolingof a process gas stream while reciprocating AMRLs need at least two setsof dual regenerators with proper phasing in/out of the magnetic fieldwith three-way valves to provide continuous bypass gas flow into theprocess heat exchangers.

In certain embodiments described herein, the systems and processes canprovide refrigeration between 20 K and 280 K with an apparatus utilizingrotary wheels or belts carrying regenerators comprised of layeredferromagnetic materials with Curie temperatures between 293 K and 50 K.The processes and systems further utilize bypass flow of a portion ofcooled heat transfer fluid (e.g., a gas) to pre-cool a separate processstream to be liquefied.

To make a highly efficient liquefier for hydrogen or other processgases, several features should be used in its design. These featuresinclude:

-   -   Use an inherently efficient thermodynamic cycle;    -   Use an efficient work input device or mechanism;    -   Use an efficient work recovery device or mechanism;    -   Insure small temperature approaches for heat transfer between or        among streams or between solids and streams;    -   Use high specific area and highly-effective regenerative and/or        recuperative heat exchangers;    -   Keep pressure drops for heat transfer gas flows and process gas        flow very low;    -   Invoke low longitudinal thermal conduction mechanisms via        material and geometry choices;    -   Minimize frictional and parasitic heat leak mechanisms; and    -   Specifically for hydrogen, perform ortho-to-para conversion at        the highest possible temperature during cooling in the process        heat exchangers.

The processes and systems disclosed herein provide more efficienthydrogen liquefaction by integrating one or more AMRR stages (e.g., 2-4)with bypass flow to continuously cool a single hydrogen process streamto create a magnetocaloric hydrogen liquefier (MCHL) or active magneticregenerative liquefier (AMRL) with much higher FOM than conventionalliquefiers. In such AMRL designs rejection and absorption of heat areachieved by the temperature increase or decrease of magneticrefrigerants in regenerators upon isentropic magnetization ordemagnetization combined with reciprocating flow of heat transfer gas.The cycle steps that magnetic refrigerants in an active magneticregenerator (AMR) execute are: i) magnetize with no heat transfer gasflow; ii) cold-to-hot heat transfer gas flow at constant magnetic highfield; iii) demagnetize with no heat transfer gas flow; and iv)hot-to-cold heat transfer flow at constant low or zero field. The AMRcycle of one or more refrigerants thermally connected by heat transferfluid (e.g., a gas) in AMRR stages can be used to design excellentliquefiers whose potential for high performance comes from:

-   -   Reversible nature of magnetization-demagnetization steps in an        AMR cycle at hertz frequencies for certain magnetic        refrigerants. In contrast, it is inherently difficult to        reversibly achieve high compression ratios, high throughput, and        high efficiency in gas compression because of fundamentally poor        thermal conductivity of low-density gases such as hydrogen or        helium;    -   Naturally efficient work-recovery mechanisms, e.g., in rotary        magnetic wheel or belt configurations large attractive magnetic        forces on magnetic materials going into the high field region        almost balance slightly larger attractive magnetic forces on        identical but slightly colder magnetic materials coming out of        the high field region. This is in contrast to limited        gas-compression-work recovery by much-colder isentropic        expanders in gas-cycle devices. To achieve highly efficient        cycles the temperature of work input must be reasonably close to        the temperature of work recovery for the entire liquefier        temperature span, i.e., from near room temperature to ˜20 K for        hydrogen which can be done with good AMRR designs;    -   Efficient internal heat transfer between porous working        refrigerant solids and flowing heat transfer fluids (e.g., a        gas) in AMR cycles can maintain small temperature differences at        all times during the cycle by using geometries with high        specific areas such as ˜10,000 m²/m³ in high-performance        regenerators;    -   Efficient cooling of the hydrogen process gas and the AMRR heat        transfer gas. This is a critical element of efficient liquefier        design. The real work required to operate a single-stage AMRR        (or any other type of single-stage refrigerator between 280 K        and 20 K) as a hydrogen liquefier will be at least 4 times        larger than the ideal work of hydrogen liquefaction. The huge        impact on FOM of this single design feature illustrates the        importance of reduction of approach temperatures in process heat        exchangers in liquefiers of hydrogen and other gases such as        helium, nitrogen, and natural gas. Conventional gas cycle        liquefiers with only two to four heat exchanger stages        inherently limit their FOM to about 0.50 before other real        component inefficiencies are incorporated. Reducing the approach        temperatures in process heat exchangers by using counterflowing        bypass flow of a small percentage of heat transfer gas is a        unique feature of AMRL designs to achieve a FOM greater than        0.5. The novel processes and systems disclosed herein        substantially reduce the number of AMRR stages required for        higher FOM as explained more fully below;    -   High energy density from use of solid refrigerants in compact        regenerative beds can become high power densities with AMR        cycles at hertz frequencies; and    -   Safe, reliable, durable, compact, and cost-effective devices.

The above-explained desired features can be achieved by incorporatinginto the systems and processes at least one, and preferably acombination, of the following inventive aspects disclosed herein:

-   -   Continuous bypass flow to continuously pre-cool the process gas        stream. The bypass gas flow is determined by the amount        necessary to completely pre-cool the process gas stream while        maintaining small 1-2 K temperature approaches between bypass        gas and process gas;    -   The heat capacity of the magnetic refrigerant changes with the        magnetic field, especially in the temperature region from the        Curie temperature to ˜25-30 K lower. Therefore, the thermal        mass, or heat capacity multiplied by the refrigerant mass, will        also vary. To take advantage of this phenomena unique to        magnetic refrigeration the mass flow rate of heat transfer gas        in the hot to cold flow region of the magnetic wheel must be        several percent (e.g, 2-6%, more particularly 2%, 3%, 4%, or 5%)        larger than the mass flow rate of heat transfer gas in the cold        to hot flow region of the same wheel to balance (i.e.,        equivalent or close to the same) the different thermal mass of        the magnetic refrigerant below their Curie temperatures in high        and low magnetic field;    -   The temperature difference between the bypass heat transfer        first cold inlet temperature and the process gas first cold exit        temperature is 1 to 5 K, more particularly 1 to 2 K;    -   The magnetic refrigerant operates at or below its Curie        temperature throughout an entire active magnetic regeneration        cycle because this is the region where the difference of thermal        mass between magnetized and demagnetized magnetic refrigerants        is maximized; and/or    -   The sensible heat of the process gas is entirely removed by the        bypass flow heat exchanger.

Certain embodiments of the novel processes and systems include the useof two dual rotary sets of identical rotary active magnetic regeneratorswith pressurized helium as a circulating common heat transfer gas tocontinuously and simultaneously execute the 4-steps of the AMR cycles atdifferent sections of rotating AMRR; i.e. as several regenerators aremagnetized in the high magnetic field region of a rotary AMRR, severalothers are demagnetized in the low-magnetic field region. Theregenerators of the rotary configuration in the two magnetic fieldregions are oriented opposite to each other such that circulating heliumheat transfer gas flows from hot-to-cold temperatures in thedemagnetized regenerators and simultaneously from cold-to-hottemperatures in the magnetized regenerators. For example, severalidentical regenerators attached to a belt, chain or wheel rim aremagnetized simultaneously while another equal number of identicalregenerators are demagnetized. Similarly, the heat transfer gas iscausing the hot-to-cold flow in several demagnetized regenerators at thesame time as heat transfer gas in an opposite part of the rotationalpath is causing the cold-to-hot flow in several magnetized regenerators.The “several” regenerators executing the different steps of the AMRcycle comprise the “set”. Each regenerator in a given ‘set’ executingone of the steps of the AMR cycle has an identical regenerator in the‘set’ executing the other three steps of the AMR cycle. In thisinstance, there are several “dual” regenerators comprised of any tworegenerators executing the opposite step in the AMR cycle. The rotaryregenerators in the high and low field regions may be separated by acold heat exchanger where the small parasitic heat leak is continuouslyabsorbed and several percent of the cold heat transfer gas from thehot-to-cold flow out of the demagnetized regenerator is sent into thebypass flow heat exchanger before the remaining heat transfer gas entersthe magnetized regenerator for the cold-to-hot flow (see FIGS. 1 and 2).Thus, the rotary geometry allows the four AMR cycle steps to existsimultaneously because at a given point in time, each of the AMR cyclesteps is occurring in a portion of the AMRR stage.

The embodiments of the novel processes and systems described hereinutilize the difference between thermal mass of ferromagneticrefrigerants below their Curie temperatures when magnetized anddemagnetized to enable use of bypass flow. The amount of bypass flowresults from the additional heat transfer gas required to changedemagnetized refrigerant temperatures through a regenerator in thehot-to-cold flow step of the AMR cycle over the heat transfer gasrequired to change magnetized refrigerant temperatures through its dualmagnetized regenerator in the cold-to-hot flow step of the AMR cycle.The larger the difference in thermal mass, the larger the amount ofbypass flow required in an optimized AMRR. Because the thermaldifference increases with difference in magnetic field during the AMRcycle, the highest practical magnetic field changes from high fieldregions at 6-8 T to low field regions at 0 to 0.3 T, preferably a valuesuch as, for example, 7 T to 0.3 T are desired. Maximum utilization ofthis feature is accomplished by operating each ferromagnetic refrigerantbelow its Curie temperature throughout its entire AMR cycle whichrequires maintaining the average T_(HOT) of each refrigerant during itsAMR cycle at least ΔT_(HOT) below its respective Curie temperature.Further, because the magnetic field-dependent thermal mass differencealso decreases monotonically as the temperature of each magneticrefrigerant decreases below its respective Curie temperature in theregenerator, the average temperature difference between average T_(HOT)and average T_(COLD) of each layer of magnetic material within aregenerator of an AMRR stage is chosen to be about 20 K. In certainembodiments, the operating temperature span (average T_(HOT)−averageT_(COLD)) of each refrigerant in the AMRRs is chosen to be ˜20-K tomaximize difference in thermal mass of the ferromagnetic refrigerants tomaximize the possible bypass flow rate. Further, over the 20-30 Ktemperature span below the Curie temperature the adiabatic temperaturechange of each magnetic refrigerant for a given magnetic field changedecreases with temperature to closely match the 2^(nd) law ofthermodynamics requirements of highly efficient thermodynamicrefrigeration cycles, i.e. T_(COLD)=ΔT_(HOT)*T_(COLD)/T_(HOT).

The helium bypass gas flow rate for each AMRR stage is calculated fromcomplete enthalpy balance between that of the desired hydrogen processgas flow rate for a particular AMRL liquefaction rate, e.g. kg/day, andthe enthalpy of the helium bypass gas flow rate in the counterflowbypass-gas to process-gas micro-channel or other highly-effective heatexchanger. This novel feature enables the sensible and/or latent heatsof the hydrogen gas to be continuously and entirely removed by thewarming helium bypass gas rather than in each cold heat exchanger (CHEX)of AMRR stages of the liquefier. The only remaining thermal load in eachCHEX is from small parasitic heat leaks, very small process stream loadsdue to residual temperature approaches in real process heat exchangers,and rejected thermal energy from the hot side of the next colder AMRRstage in a series configuration of a hydrogen liquefier (See FIG. 2).Use of this design feature applies no matter what hydrogen processstream flow rate is desired, i.e., the helium gas bypass flow rate issimply increased to completely cool the hydrogen process stream towithin 1-2 K of the coldest temperature of the particular AMRR stagebeing considered. For example, the hydrogen process stream can be cooledto the bubble point temperature for a specified pressure (e.g., ˜20 Kfor LH₂ at 0.1013 MPa). The average T_(COLD) of the coldest AMRR stagewill be 1-2 K below the LH₂ temperature. The variable in this designprocedure is the helium bypass flow; as it increases with increasing LH₂liquefaction, the helium heat transfer flow through the magneticregenerators increases which in turn increases with the size of the AMRRstages.

In this design procedure, the helium bypass flow rate is determined bythe AMRL hydrogen liquefaction rate. In turn, the helium bypass gas flowrate is an optimum small fraction of the helium heat transfer gas flowrate for the AMRR stage. The heat transfer gas flow rate is directlycoupled to the detailed design variables of the AMRR including thenumber and mass of magnetic refrigerants, adiabatic temperature changes,magnetic field change, heat capacity of the refrigerants, the cyclefrequency, and temperature profile from T_(HOT) to T_(COLD) within theregenerator that determines the fraction of the active magneticregenerator that cools below the average T_(COLD) each cycle. With anoptimum hot-to-cold flow rate of helium heat transfer gas through theactive magnetic regenerators the average cooling power of thedemagnetized regenerator (using Gd as an example of an excellentmagnetic refrigerant) is given by:{dot over (Q)} _(Gd)(T _(COLD))=νFr _(COLD) M _(Gd) C _(Gd)(T _(COLD) ,B_(0.6T))ΔT _(CD)(T _(COLD))where {dot over (Q)}_(d) (T_(COLD)) is the cooling power in W, ν is theAMR cycle frequency in Hz, Fr_(COLD) is a blow-averaged dimensionlessfraction of the regenerator that is colder than the average T_(COLD) ofthe demagnetized regenerator before the hot-to-cold blow of the heliumheat transfer gas, M_(Gd) is the mass of Gd in a flow sector of therotary wheel regenerator in kg, C_(Gd) is the total heat capacity of Gdat T_(COLD) and the low magnetic field after demagnetization in J/kg K,ΔT_(CD) is the adiabatic temperature change upon demagnetization fromhigh field to low field in K. All the variables in this equation areknown except Fr_(COLD). This parameter depends on the axial temperatureprofile of an AMR that depends upon the cold thermal load, the heattransfer gas flow rate, and the percentage of bypass flow. Numericalsimulation of axial temperature profiles for magnetic regenerators as afunction of bypass flow of helium heat transfer gas can be predicted bysolving the partial differential equations that describe AMRperformance. A linear temperature profile is a good approximation foroptimum helium heat transfer gas and percentage bypass flow. Experimentsconfirm the numerical predictions that 3-12% bypass is the typical rangedepending upon the magnetic refrigerant and magnetic field changes. Thehelium heat transfer gas flow rate is given by dividing the coolingpower of the regenerator by the heat capacity of helium at constantpressure times ΔT_(CD)/2 in kg/s.

Certain embodiments of the novel processes and systems have bypass flowof a few percent of cold helium gas (e.g., 3 to 12% of the total heattransfer gas in the hot-to-cold flow through the demagnetizedregenerator, more particularly 6%) to continuously pre-cool the hydrogenprocess stream thus reducing the number of AMRR stages in an efficientH₂ liquefier from 6-8 stages without bypass flow to 3-4 stages withbypass flow. It is obvious fewer AMRR stages using bypass flow tocontinuously pre-cool the hydrogen process stream will also requiresubstantially less magnetic refrigerant for an equivalent liquefactionrate. Continuous cooling of the hydrogen process stream in a liquefieressentially eliminates a very large source of irreversible entropygeneration and thereby increases the FOM of the liquefier significantly.From this description it is apparent that the flow rate of bypass heattransfer gas is determined by complete removal of the sensible andlatent heats from the process stream which in turn determines the totalhelium heat transfer flow rate for the AMRR stage given the percentageof bypass flow allowed by the thermal mass differences in the magneticregenerator which in turn determines the mass of the magneticregenerator given the ΔT_(COLD) from the magnetocaloric effect. Thisnovel design process minimizes the number of AMRR stages and mass ofmagnetic refrigerants in liquefiers for hydrogen and other gases.

Certain embodiments of the novel processes and systems use layeredactive magnetic regenerators for enabling larger differences between theaverage temperatures T_(HOT) and T_(COLD) necessary to use fewer stagesin the new hydrogen liquefier design. The magnetic regenerators arefabricated with multiple longitudinally or radially-layered magneticrefrigerants located such that the Curie temperature of each refrigerantis above the average AMR-cycle hot temperature T_(HOT) by ΔT_(HOT) atthat axial location in the regenerators in steady-state operation tomaximize thermal mass differences and thereby percentage of bypass flow.All the refrigerants in the AMRR individually execute small magneticBrayton cycles as they are alternately magnetized and demagnetized bythe magnetic field and connected together from T_(HOT) to T_(COLD) bythe flowing helium heat transfer gas. This coupling allows the overalltemperature span of an AMRR to be many times adiabatic temperaturechanges from the magnetocaloric effect of each magnetic refrigerant. Thethermomagnetic properties of properly layered refrigerants mustsimultaneously have entropy flows that satisfy the 2nd law ofthermodynamics with allowance for generation of irreversible entropy andeffects of bypass flows.

An AMR cycle has four steps: magnetization of one set of active magneticregenerators in the rim of the wheel in FIG. 1 of the same stage withoutflow of heat transfer fluid; flow of heat transfer fluid fromcold-to-hot through the magnetized beds; demagnetization of this sameset of beds while there is no flow of heat transfer fluid; and flow ofheat transfer fluid from hot-to-cold through the demagnetized beds. FIG.1 illustrates that four sets of layered regenerators in the rim of thewheel in the AMRR stage undergo the four steps of the AMR cycle, but 180degrees out of phase with a similar set of regenerator beds. After theactive magnetic regenerators (AMR) in the rim of the wheel in FIG. 1have executed several hundred cycles, i.e. in 10-15 minutes, the layeredactive magnetic regenerators in the rim of the wheel in FIG. 1 will havean average dynamic temperature gradient from T_(HOT) to T_(COLD) alongthe flow axis of the active magnetic regenerators, i.e., in the radialdirection through the rim of the wheel in FIG. 1.

The magnetic refrigerants in the AMR beds have a difference in thermalmass which is the product of heat capacity per unit mass times the massof magnetic refrigerant (or just heat capacity in this case because themass of magnetic material in a magnetic regenerator doesn't depend upontemperature or magnetic field). The heat capacity of a ferromagneticmaterial below the Curie temperature (ordering temperature) is smallerin higher magnetic fields than at lower or zero magnetic fields.However, this difference switches at the Curie temperature because theheat capacity in higher magnetic fields decreases slowly as thetemperature increases while the heat capacity in low or zero fieldsdrops sharply at the Curie temperature such that the heat capacity athigher fields becomes larger than the heat capacity in lower or zeromagnetic fields. This means the difference in thermal mass between amagnetized AMR bed and a demagnetized AMR bed changes sign at the Curietemperature and the net difference in thermal mass for an AMR cyclespanning across the Curie temperature rapidly decreases with increasingtemperature. Therefore, the optimal amount of bypass flow for an AMRcycle that extends above the Curie temperature will rapidly decrease tozero. Simultaneously an AMR cycle operated this way will become lessefficient due to increased intrinsic entropy generation in such an AMRcycle and due to insufficient bypass flow to pre-cool the same amount ofhydrogen process gas. In the design of the novel processes and systemsdisclosed the importance of selecting and controlling the hot sinktemperature and temperature span to maximize the difference in thermalmass (and thereby the amounts of bypass flow) is recognized. First, thedynamic T_(HOT) is always ΔT_(HOT) less than the Curie temperature ofthe magnetic refrigerant at the hot end of the regenerator (i.e., theouter-most refrigerant in the layered rim of the wheel in FIG. 1) at itsmaximum during the magnetization step of the AMR cycle. T_(HOT) is theenvironmental temperature where the heat is dumped. The dynamic T_(HOT)is the increase in temperature caused by inserting the regenerator intothe magnetic field. The maximum dynamic T_(HOT) depends on where it isin the cycle, but generally the maximum is T_(HOT)+ΔT_(HOT). This can bedone by setting a fixed heat sink temperature to anchor T_(H) which inturn yields the largest difference in thermal mass between high and lowmagnetic fields. The second aspect of the difference in thermal mass inhigh and low magnetic fields is that it decreases steadily as the coldtemperatures in the regenerator decrease below the Curie temperature (s)of the magnetic refrigerants. Hence, the magnetic materials in an AMRbed must operate in temperature spans when magnetized ofT_(H)+ΔT_(HOT)≤T_(Curie) and T_(C)+ΔT_(COLD) equal to ˜20 K<T_(Curie)and when demagnetized, between T_(H)−ΔT_(HOT) and T_(C)−ΔT_(COLD) whichare ˜20 K apart. T_(C) represents cold temperatures of a slice ofmagnetic regenerator at any point in the AMR as it executes its tinymagnetic Brayton cycle. ΔT_(COLD) represents the temperature drop causedby the magnetocaloric effect when the regenerator is removed from themagnetic field. If larger temperature spans with optimum differences inthermal mass are desired (as required for very high FOM), layers ofmagnetic materials with descending Curie temperatures must be used inthe AMR bed.

For example, Gd metal is an excellent ferromagnetic refrigerant that hasa Curie temperature of about 293 K. With ˜6.5-Tesla magnetic fieldchanges [6.8 T to 0.3 T], the adiabatic temperature change ΔT_(HOT) isabout 12-13 K so we maintain T_(HOT) to be 280 K so the maximumtemperature during its AMR cycle is 280 K+12 K or 292 K. Thistemperature is indicated in FIG. 1 and FIG. 2. The hot heat sinktemperature is shown as 278 K-280 K in FIGS. 1 and 2. During a completerotation of the wheel in FIG. 1, Gd will be other outermost layer ofrefrigerant in the rim-shaped layered regenerator and its temperaturewill change from ˜292-293 K just as it enters the high field region anddrop to ˜280 K as it leaves the high field region and drop further to˜270 K as it enters the low/zero field region and increases to ˜280 K asit leaves the low/zero field region and then increase to ˜293 K as itenters the high field region again. The average of the Gd temperature asit rotates is ˜280 K which is the average T_(HOT) of the AMRR stage. Asimilar shaped dynamic temperature cycle is executed by different layerswithin the wheel. The temperature span is the difference between theaverage T_(HOT) and the average T_(COLD). In the AMRR stage shown inFIG. 1 the temperature span is 122 K to 280 K. Other AMRR stages in amulti-stage liquefier will have different spans as indicated in FIG. 2.

For each layer of magnetic refrigerant, the value of T_(H) is theaverage of the dynamic temperature at the edge of the layer in the rimof the wheel illustrated in FIG. 1. It varies through a layeredregenerator and can be measured by a tiny temperature sensor (such as athermocouple) inserted into the regenerator during rotation of the wheelthat will show the small local magnetic Brayton cycle or AMR cycle.

As described above, a portion of the cold heat transfer fluid from eachAMRR stage is returned to the hot heat sink via bypass flow. Each stageof the rotary embodiments of an AMRR has sets of dual AMRs forcontinuous bypass flow to the process heat exchanger during all steps ofthe AMR cycle with each AMRR stage sized to ensure the bypass flow fromeach stage completely cools the process gas (hydrogen) to the coldtemperature of the respective stage. This is a powerful design featurebecause it allows the approach temperatures between the counter-flowinghelium bypass flow and the ‘equilibrium’ hydrogen gas in the processheat exchanger with embedded ortho-para catalysts to be 1-2 K or less atall times. The phrase “approach temperature” refers to the temperaturedifference between the helium bypass flow and hydrogen gas in theprocess heat exchanger at the bypass gas flow entrance of the bypassheat exchanger.

Illustrative embodiments of the AMRR stages are rotary designs with setsof dual regenerators that are simultaneously executing the four steps ofthe AMR cycle at all times during the rotational cycle of 0.5 to 1Hertz. One embodiment shown, for example, in FIG. 1, has four differentregions in the rotary design allows continuous flow of the heat transfergas through some demagnetized regenerator beds (the identicalregenerators in the low/zero field region) and some magnetizedregenerator beds (the identical regenerators in the high field region)and no flow through the regions where the magnetic field is eitherincreasing or decreasing. The bypass heat transfer fluid flow iscontinuously sent to the process heat exchanger from the cold heattransfer fluid flowing out of the cold duct in the low field region intothe cold duct in the high field region to maintain steady-state flow andthus the very small 1 to 5 K, more particularly 1-2 K, approachtemperatures at all times and locations in the process heat exchanger. Amajor improvement is that the use of bypass flow of only a few percentof cold helium gas to pre-cool the hydrogen process stream reduces thenumber of AMRR refrigeration stages in an efficient H₂ liquefier from 6to 3 or 4.

Good magnetic refrigerants have large magnetic moments to providemaximum entropy change from changes in magnetic field. The accompanyingmagnetocaloric effect of a good material is confined to a finitetemperature range around its magnetic ordering temperature where themagnetic entropy is strongly temperature and field dependent. To takemaximum advantage of bypass flow it is important to maximize thedifference between the high-field and low-field thermal mass of magneticrefrigerants. The thermomagnetic properties of the refrigerants mustsimultaneously satisfy numerous other criteria such as: i) satisfyingthe adiabatic temperature changes as a function of temperature tosatisfy the 2nd law of thermodynamics and ii) allowance for inevitablecreation of some irreversible entropy even in the best optimizedregenerator designs.

Gadolinium is an excellent magnetic refrigerant and has been generallyaccepted as the reference material against which other refrigerants arecompared. It has a simple ferromagnetic ordering temperature of ˜292 Kand exhibits an adiabatic temperature change of ˜2 K/Tesla overpractical magnetic field strengths (up to ˜8 T). It also has a largedifference in field-dependent thermal mass just below its Curietemperature. Introduction of alloying additions of another lanthanidemetal reduces the magnetic-ordering temperature of Gd without mucheffect on the total magnetic moment per unit volume and the change inmagnetization with temperature near a sharp ordering temperature.

Homogeneous alloys of Gd with other rare earth metals (Tb, Er, Dy, Ho)or Y make superior magnetic refrigerants as well. Other potential rareearth elemental refrigerants such as Ho and Er have more complexmagnetic ordering phenomenon but when alloyed with Gd these effects tendto be reduced at high magnetic fields. The addition of non-magnetic Y toGd reduces the adiabatic temperature change of Gd gradually butsimultaneously decreases the magnetic ordering temperature so the simpleferromagnetism of Gd is preserved down to about 200 K.

Key features or suitable refrigerant materials include:

-   -   Use ferromagnetic materials that operate below their Curie        temperature throughout their entire AMR cycle;    -   Maintain average T_(HOT) at least ΔT_(HOT) below the Curie        temperature of the uppermost layer of magnetic material in a        regenerator; this applies to each layer of magnetic material in        the regenerator with correspondingly lower cycle temperatures;    -   Average temperature difference between T_(HOT) and T_(COLD)        should be ˜20 K per layer of magnetic refrigerant;    -   Spanning from 280 K to 120 K in one AMRR stage requires 8        refrigerants to be combined into optimally layered regenerators.    -   Layering must have smooth flows of energy and entropy at        transitions between layered refrigerants along the longitudinal        axis of the regenerator.

Illustrative magnetic refrigerants include those shown below in Table 1.

Operating Ordering Temperature Span Temperature Material K K Gd 280-260293 Gd_(0.90)Y_(0.10) 260-240 274 Gd_(0.30)Tb_(0.70) 240-220 253Gd_(0.69)Er_(0.31) 220-200 232 Gd_(0.02)Tb_(0.98) 220-200 233Gd_(0.32)Dy_(0.68) 200-180 213 Gd_(0.66)Y_(0.34) 200-180 213Gd_(0.39)Ho_(0.61) 180-160 193 Gd_(0.59)Y_(0.41) 180-160 193Gd_(0.15)Dy_(0.85) 180-160 193 Gd_(0.42)Er_(0.58) 160-140 173Gd_(0.27)Ho_(0.73) 160-140 173 Gd_(0.16)Ho_(0.84) 140-120 153Gd_(0.34)Er_(0.66) 140-120 152 Gd_(0.23)Er_(0.77) 120-100 132(Ho_(0.80)Gd_(0.20))Co₂ 120-100 130

Illustrative ortho H₂ to para H₂ catalysts for use in the bypass flowprocess heat exchangers include, but are not limited to, activatedcarbon; ferric oxide (Fe₂₃); chromic oxides (Cr₂O₃ or CrO₃); Ni metaland Ni compounds (Ni²⁺); rare earth metals and oxides such as Gd₂O₃,Nd₂O₃, and Ce₂O₃; Pt; and Ru. Activated carbon and ferric oxide areparticularly preferred. The catalysts may be employed in lowconcentrations on alumina or similar substrates and placed directly intothe hydrogen process stream either in or near the process heatexchangers.

In certain embodiments the catalyst may be incorporated into amicro-channel or tube-in-tube GH₂ process heat exchangers in counterflowwith the cold helium bypass flows from the AMRR stage(s) to maintain‘equilibrium’ hydrogen continuously as the hydrogen is cooled. Thiscontinuously removes the exothermic heat of conversion at the highestpossible temperatures necessary to maintain very high FOM in the overallliquefier. Thus, certain embodiments of the novel processes and systemscan provide a FOM of at least 0.6, more particularly at least 0.7, andmost particularly at least 0.75.

The rotary AMRR apparatus includes an annular bed 1 of at least oneporous magnetic refrigerant material. As shown in FIG. 1, the rotaryAMRR apparatus is divided into four sections (listed in order of wheelrotation): (i) a high magnetic field section in which the heat transfergas flows from a cold side to a hot side through the magnetized bed(s),(ii) a first no heat transfer gas flow section in which the bed(s) aredemagnetized, (iii) a low magnetic or demagnetized field section inwhich the heat transfer gas flows from a hot side to a cold side throughthe demagnetized bed(s), and (iv) a second no heat transfer gas flowsection in which the bed(s) are magnetized. Seals are provided in the noheat transfer gas flow sections to prevent the heat transfer gas flow.The magnetic refrigerant bed may be divided into compartments 6 whereinthe compartments may include differing magnetic refrigerants relative toother compartments.

The rotary AMRR apparatus includes a rotating wheel that includes aninside hollow annular rim 2 (inner housing and flow duct wall) and anoutside hollow annular rim 3 (outer housing and flow duct wall). A hotheat transfer fluid (HTF) (e.g., helium gas) is introduced into theoutside rim 3 of the rotary AMRR apparatus via an HTF inlet ductprovided in the low magnetic or demagnetized field section (iii). Thehot HTF in the outside rim 3 has a steady-state circumferentiallyaverage temperature that, for example, may be 280-285 K. However, thelocal temperature at a given time and location in the AMR cycle maydiffer from the steady-state circumferentially average temperature. Thehot HTF flows in a radial direction through the low magnetic ordemagnetized bed, cooling the HTF. The cooled heat transfer fluid exitsthe low magnetic or demagnetized field section (iii) via an HTF outletduct and into the inside rim 2. The HTF radial flow is shown by thearrows 4 in the low magnetic or demagnetized field section (iii). Thecold HTF in the inside rim 2 has a steady-state circumferentiallyaverage temperature that, for example, may be 125-130 K. However, thelocal temperature at a given time and location in the AMR cycle maydiffer from the steady-state circumferentially average temperature. Theinside rim 2 is fluidly coupled via an HTF outlet duct and a conduit toan inlet of an optional cold heat exchanger (CHEX). If desired, the CHEXis for the reject heat from a colder AMRR stage and for very smallparasitic heat leaks. As can be seen the approach temperaturedifferential in the CHEX is 1 K.

The heat transfer fluid exits the CHEX and into a T-junction in which aportion of the heat transfer fluid bypasses the high magnetic fieldsection (i) and instead is directed to an inlet of a bypass gas heatexchanger. The flow at the T-junction may be controlled a bypass flowcontrol valve. In certain embodiments, 3-12%, particularly less than12%, more particularly less than 8%, and most particularly 6%, of theheat transfer fluid is diverted to the bypass gas heat exchanger. Theremaining heat transfer fluid is introduced as the cold flow into theinside rim 2 at the high magnetic field section (i) via an HTF inletduct.

The cold HTF flows in a radial direction through the high magnetizedbed, heating the HTF. The hot HTF exits the high magnetic field section(i) via an HTF outlet duct and into the outside rim 3. The HTF radialflow is shown by the arrows 5 in the high magnetic field section (i).The hot HTF exits the high magnetic field section (i) and is introducedvia a conduit to into a hot heat exchanger (HHEX). The HHEX cools theheat transfer fluid down to a suitable temperature for introduction asthe hot flow into the low magnetic or demagnetized field section (iii).

As mentioned above, the bypass HTF is introduced into a bypass HEX. Thebypass HTF cools the process gas that is also introduced into the bypassHEX. In certain embodiments, the bypass HEX includes at least one orthoH₂ to para H₂ catalyst. The sensible heat in the process gas stream isremoved only via the bypass HEX. In other words, no other heatexchangers are required to remove the sensible heat (as mentioned above,the CHEX only removes the reject heat from a colder AMRR stage and verysmall parasitic heat leaks). As can be seen the approach temperaturedifferential in the bypass HEX is 1 K.

The bypass HTF exiting the bypass HEX is mixed with the hot HTF flowexiting the high magnetic field section (i). The mixed bypass HEX andhot HTT flow is introduced into the HHEX.

FIG. 2 is a schematic of a 3-stage AMRR with continuous bypass flow in aseries configuration as a H₂ liquefier. Process gas is introduced intothe first stage in which it passes through a first bypass heatexchanger. In certain embodiments, prior to the first bypass heatexchanger the process gas passes through a hot heat sink chiller. Thehot heat sink chiller or the chiller hot sink is the anchor point forthe system. The “anchor point” is the temperature of the ambient orenvironment that the heat is dumped into. Partially cooled process gasfrom the first stage bypass heat exchanger is introduced into a secondstage bypass heat exchanger. Further cooled process gas from the secondstage bypass heat exchanger is introduced into a third stage bypass heatexchanger. In each respective bypass heat exchanger the heat flow (Qdot)is equal to the mass flow (mdot) times the enthalpy differential (Ah).Each respective AMRR module (AMRR-1, AMRR-2, and AMRR-3) may be the sameor similar to the single stage AMRR shown in FIG. 1.

FIG. 3 is a block process flow diagram of gas H₂ (GH2) to liquid H₂(LH₂) liquefier facility with multistage AMRR with bypass flow. FIG. 3depicts an illustrative GH2 source which may be, for example, ahydrocarbon feedstock (e.g., methane) and/or water from which GH2 isproduced via a steam methane reformer (SMR) or an electrolyzer. Incertain embodiments, the GH2 may pass through a cryogenic temperatureswing adsorption (TSA) module for GH2 purification.

FIG. 4 discloses a helium heat transfer gas subsystem and the use ofmultiple three-way flow control valves to integrate a single heattransfer gas circulating pump, a single hot heat rejection heatexchanger, a single bypass gas heat exchanger with four active magneticregenerators. The magnets are shown displaced from each other but thatis only for convenience of illustrating thedemagnetization/magnetization steps of the AMR cycle where no flowoccurs in either regenerator. The gas flow lines are also drawn forconvenience rather than vertically and close to each other so theregenerators can easily move up and down in and out of high magneticfield region to low field region. Alternatively, the regenerators couldremain fixed and the magnets moved reciprocatively so the samegeometrical constraints exist.

FIG. 4 is a snapshot in time of four identical layered magneticregenerators executing AMR cycles with four steps for each regenerator:i) cold-to-hot flow while magnetized; ii) no flow while beingdemagnetized; iii) hot-to-cold flow while demagnetized; and iv) no flowwhile being magnetized. In steady-state operation regenerators 21-24 areoperating the same cycle but 90 degrees out of phase with each other inthe sequence of 21,23,22,24. An important feature of this integratedquad design is the continuous flow of a percentage of heat transfer gasthrough the bypass heat exchanger. The bypass flow is established by therequirement that it must be large enough to completely pre-cool adesired flow rate of process stream from a hotter temperature to acolder temperature such as 280 K to 120 K.

In FIG. 4, regenerator 21 is magnetized and has cold-to-hot helium gasflow through it; regenerator 22 is demagnetized and has hot-to-coldhelium gas flow through it [the temperature of the helium is set by thechiller that sets the outlet temperature of the helium in the hot heatrejection heat exchanger or T_(HOT) [in this example it is 280 K].Regenerator 22 provides cold helium at a blow-averagedT_(COLD)−ΔT_(COLD)/2 that supplies the cold helium flow into the bypassheat exchanger and a flow to the cold heat exchanger [which could bevery small if only parasitic heat leaks are present and there is nolower AMRR stage]. Regenerator 23 has no helium flow and is beingmagnetized; Regenerator 24 is being demagnetized and has no helium floweither. Note that the three-way valves, flow control valves, and checkvalves are indicated in the flow loop. There is a single continuouslycirculating helium pump just before the chiller HEX near the hottemperature. The helium heat transfer gas flows can be traced out byfollowing the open segments in the three-way valves and the same type ofline (solid, dotted, dashed, and dot-dashed). As each regenerator isdemagnetized, the hot-to-cold flow will provide the bypass flow for W ofthe AMR cycle to ensure the bypass heat exchanger continuously cools theprocess gas stream.

Illustrative embodiments are described below in the following numberedclauses:

1. A process for liquefying a process gas comprising:

introducing a heat transfer fluid into an active magnetic regenerativerefrigerator apparatus that comprises (i) a high magnetic field sectionin which the heat transfer fluid flows from a cold side to a hot sidethrough at least one magnetized bed of at least one magneticrefrigerant, (ii) a first no heat transfer fluid flow section in whichthe bed is demagnetized, (iii) a low magnetic or demagnetized fieldsection in which the heat transfer fluid flows from a hot side to a coldside through the demagnetized bed, and (iv) a second no heat transferfluid flow section in which the bed is magnetized;

continuously diverting a bypass portion of the heat transfer fluid fromthe cold side of the low magnetic or demagnetized field section into abypass flow heat exchanger at a first cold inlet temperature; and

continuously introducing the process gas into the bypass flow heatexchanger at a first hot inlet temperature and discharging the processgas or liquid from the bypass flow heat exchanger at a first cold exittemperature;

wherein the temperature difference between the bypass heat transferfirst cold inlet temperature and the process gas first cold exittemperature is 1 to 5 K.

2. The process of clause 1, wherein the temperature difference is 1 to 2K.

3. The process of clause 1 or 2, further comprising introducing thenon-bypassed portion of the heat transfer fluid into the cold side ofthe magnetized bed in the high magnetic field section.

4. The process of any one of clauses 1 to 3, wherein the bypass portionconstitutes 3 to 12% of the total heat transfer fluid exiting the coldside of the low magnetic or demagnetized field section.

5. The process of any one of clauses 1 to 4, wherein the magneticrefrigerant operates at or below its Curie temperature throughout anentire active magnetic regeneration cycle.

6. The process of clause 5, wherein the magnetic refrigerant operates ina range from less than its Curie temperature to 32K below its Curietemperature throughout an entire active magnetic regeneration cycle.

7. The process of any one of clauses 1 to 6, wherein the sensible and/orlatent heat of the process gas are entirely removed by the bypass flowheat exchanger.

8. A process for liquefying a process gas comprising:

introducing a heat transfer fluid into an active magnetic regenerativerefrigerator apparatus that comprises (i) a high magnetic field sectionin which the heat transfer fluid flows from a cold side to a hot sidethrough at least one magnetized bed of at least one magneticrefrigerant, (ii) a first no heat transfer fluid flow section in whichthe bed is demagnetized, (iii) a low magnetic or demagnetized fieldsection in which the heat transfer fluid flows from a hot side to a coldside through the demagnetized bed, and (iv) a second no heat transferfluid flow section in which the bed is magnetized;

continuously diverting a bypass portion of the heat transfer fluid fromthe cold side of the low magnetic or demagnetized field section into abypass flow heat exchanger at a first cold inlet temperature; and

continuously introducing the process gas into the bypass flow heatexchanger at a first hot inlet temperature and discharging the processgas or liquid from the bypass flow heat exchanger at a first cold exittemperature;

wherein the magnetic refrigerant operates at or below its Curietemperature throughout an entire active magnetic regeneration cycle.

9. The process of clause 8, wherein the magnetic refrigerant operates ina range from less than its Curie temperature to 32K below its Curietemperature throughout an entire active magnetic regeneration cycle.

10. A process for liquefying a process gas comprising:

introducing a heat transfer fluid into an active magnetic regenerativerefrigerator apparatus that comprises (i) a high magnetic field sectionin which the heat transfer fluid flows from a cold side to a hot sidethrough at least one magnetized bed of at least one magneticrefrigerant, (ii) a first no heat transfer fluid flow section in whichthe bed is demagnetized, (iii) a low magnetic or demagnetized fieldsection in which the heat transfer fluid flows from a hot side to a coldside through the demagnetized bed, and (iv) a second no heat transferfluid flow section in which the bed is magnetized;

continuously diverting a bypass portion of the heat transfer fluid fromthe cold side of the low magnetic or demagnetized field section into abypass flow heat exchanger at a first cold inlet temperature; and

continuously introducing the process gas into the bypass flow heatexchanger at a first hot inlet temperature and discharging the processgas or liquid from the bypass flow heat exchanger at a first cold exittemperature;

wherein the sensible heat of the process gas is entirely removed by thebypass flow heat exchanger.

11. A process for liquefying hydrogen gas into liquid hydrogencomprising:

continuously introducing hydrogen gas into an active magneticregenerative refrigerator module, wherein the module has one to fourstages, wherein each stage includes a bypass flow heat exchanger thatreceives a bypass helium heat transfer gas from a cold side of a lowmagnetic or demagnetized field magnetic refrigerant bed at a first coldinlet temperature and discharges hydrogen gas or fluid at a first coldexit temperature; wherein the sensible heat of the hydrogen gas isentirely removed by the bypass flow heat exchanger, the magneticrefrigerant operates at or below its Curie temperature throughout anentire active magnetic regeneration cycle, and the temperaturedifference between bypass helium heat transfer first cold inlettemperature and the hydrogen gas first cold exit temperature is 1 to 2K.

12. The process of any one of clauses 1 to 11, wherein the processprovides a figure of merit (FOM) of at least 0.6, more particularly atleast 0.7, and most particularly at least 0.75.

13. The process of any one of clauses 1 to 12, wherein the bypass flowheat exchanger includes at least one ortho H₂ to para H₂ catalyst.

14. The process of any one of clauses 1 to 14, wherein the magneticrefrigerant is selected from Gd, Gd_(0.90)Y_(0.10), Gd_(0.30)Tb_(0.70),Gd_(0.69)Er_(0.31), Gd_(0.02)Tb_(0.98), Gd_(0.32)Dy_(0.68),Gd_(0.66)Y_(0.34), Gd_(0.39)Ho_(0.61), Gd_(0.59)Y_(0.41),Gd_(0.15)Dy_(0.85), Gd_(0.42)Er_(0.58), Gd_(0.27)Ho_(0.73),Gd_(0.16)Ho_(0.84), Gd_(0.34)Er_(0.66), Gd_(0.23)Er_(0.77), or(Ho_(0.80)Gd_(0.20))Co₂.

In view of the many possible embodiments to which the principles of thedisclosed processes and systems may be applied, it should be recognizedthat the illustrated embodiments are only preferred examples of theinvention and should not be taken as limiting the scope of theinvention.

What is claimed is:
 1. A process for liquefying hydrogen gas into liquidhydrogen comprising: continuously introducing hydrogen gas into anactive magnetic regenerative refrigerator module, wherein the module hasonly one, two, three or four stages, wherein each stage includes abypass flow heat exchanger having a first passage that contains ahydrogen flow, and a second passage that receives a bypass flow portionof helium heat transfer gas from a magnetic refrigerant regenerator in acold side of a low magnetic or demagnetized field region at a bypasshelium heat transfer gas first cold inlet temperature and dischargeshydrogen gas or liquid at a first cold exit temperature; wherein thehydrogen flow flows counter to the bypass pass flow portion of thehelium heat transfer, sensible heat of the hydrogen gas is entirelyremoved by the bypass flow heat exchanger in the one stage module or acombination of each bypass flow heat exchanger in each stage of the two,three or four stage module, the magnetic refrigerant regeneratoroperates at or below its Curie temperature throughout an entire activemagnetic regeneration cycle, a temperature difference between the bypasshelium heat transfer gas first cold inlet temperature and the hydrogengas first cold exit temperature is 1 to 2 K for each bypass flow heatexchanger, and the bypass flow heat exchanger of each stage includes atleast one ortho H₂ to para H₂ catalyst.
 2. The process of claim 1,wherein the magnetic refrigerant regenerator includes at least onemagnetic refrigerant is selected from Gd, Gd_(0.90)Y_(0.10),Gd_(0.30)Tb_(0.70), Gd_(0.69)Er_(0.31), Gd_(0.02)Tb_(0.98),Gd_(0.32)Dy_(0.68), Gd_(0.66)Y_(0.34), Gd_(0.39)Ho_(0.61),Gd_(0.59)Y_(0.41), Gd_(0.15)Dy_(0.85), Gd_(0.42)Er_(0.58),Gd_(0.27)Ho_(0.73), Gd_(0.16)Ho_(0.84), Gd_(0.34)Er_(0.66),Gd_(0.23)Er_(0.77), or (Ho_(0.80)Gd_(0.20))Co₂.
 3. The process of claim1, wherein the magnetic refrigerant regenerator includes at least onemagnetic refrigerant that is a material with a second order phasetransition.
 4. The process of claim 3, wherein the magnetic refrigerantregenerator operates in a range from less than its Curie temperature to32K below its Curie temperature throughout the entire active magneticregeneration cycle.
 5. The process of claim 3, wherein the at least oneortho H₂ to para H₂ catalyst is activated carbon; ferric oxide; achromic oxide; Ni metal; Ni-containing compounds; a rare earth metal; arare earth metal oxide; Pt; or Ru.
 6. The process of claim 3, whereinthe at least one ortho H₂ to para H₂ catalyst is ferric oxide.
 7. Theprocess of claim 1, wherein the magnetic refrigerant regeneratoroperates in a range from less than its Curie temperature to 32K belowits Curie temperature throughout the entire active magnetic regenerationcycle.
 8. The process of claim 1, wherein the module has only two, threeor four stages.
 9. The process of claim 8, wherein the process providesa figure of merit (FOM) of at least 0.6.
 10. The process of claim 8,wherein the magnetic refrigerant regenerator includes at least onemagnetic refrigerant selected from Gd, Gd_(0.90)Y_(0.10),Gd_(0.30)Tb_(0.70), Gd_(0.69)Er_(0.31), Gd_(0.02)Tb_(0.98),Gd_(0.32)Dy_(0.68), Gd_(0.66)Y_(0.34), Gd_(0.39)Ho_(0.61),Gd_(0.59)Y_(0.41), Gd_(0.15)Dy_(0.85), Gd_(0.42)Er_(0.58),Gd_(0.27)Ho_(0.73), Gd_(0.16)Ho_(0.84), Gd_(0.34)Er_(0.66),Gd_(0.23)Er_(0.77), or (Ho_(0.80)Gd_(0.20))Co₂.
 11. The process of claim8, wherein the magnetic refrigerant regenerator includes at least onemagnetic refrigerant that is a material with a second order phasetransition.
 12. The process of claim 8, wherein the magnetic refrigerantregenerator operates in a range from less than its Curie temperature to32K below its Curie temperature throughout the entire active magneticregeneration cycle.
 13. The process of claim 8, further comprising inthe last stage, introducing helium heat transfer gas that includes thebypass flow portion and a non-bypass flow portion into the bypass flowheat exchanger in counterflow with the hydrogen flow, flowing thenon-bypass flow portion flows through a portion of the bypass flow heatexchanger, and then returning the non-bypass flow portion to themagnetic refrigerant regenerator.
 14. The process of claim 13, whereinthe magnetic refrigerant regenerator includes at least one magneticrefrigerant that is a material with a second order phase transition. 15.The process of claim 1, wherein the at least one ortho H₂ to para H₂catalyst is activated carbon; ferric oxide; a chromic oxide; Ni metal;Ni-containing compounds; a rare earth metal; a rare earth metal oxide;Pt; or Ru.
 16. The process of claim 1, wherein the at least one ortho H₂to para H₂ catalyst is ferric oxide.
 17. The process of claim 1, whereinthe module has only three or four stages.
 18. The process of claim 17,wherein the magnetic refrigerant regenerator includes at least onemagnetic refrigerant that is a material with a second order phasetransition.
 19. The process of claim 18, wherein the at least one orthoH₂ to para H₂ catalyst is activated carbon; ferric oxide; a chromicoxide; Ni metal; Ni-containing compounds; a rare earth metal; a rareearth metal oxide; Pt; or Ru.
 20. The process of claim 1, wherein themodule has only four stages.
 21. The process of claim 20, wherein themagnetic refrigerant regenerator includes at least one magneticrefrigerant that is a material with a second order phase transition. 22.The process of claim 21, wherein the at least one ortho H₂ to para H₂catalyst is activated carbon; ferric oxide; a chromic oxide; Ni metal;Ni-containing compounds; a rare earth metal; a rare earth metal oxide;Pt; or Ru.
 23. The process of claim 1, wherein the bypass flow portionof the helium heat transfer gas constitutes 3 to 12% of the total heliumheat transfer gas flowing in the low magnetic or demagnetized fieldregion.
 24. The process of claim 1, wherein the magnetic refrigerantregenerator includes at least one magnetic refrigerant selected from Gd,a homogeneous alloy of Gd with Tb, a homogeneous alloy of Gd with Er, ahomogeneous alloy of Gd with Dy, a homogeneous alloy of Gd with Ho, or ahomogeneous alloy of Gd with Y.
 25. The process of claim 1, wherein themagnetic refrigerant regenerator includes at least one magneticrefrigerant selected from a homogeneous alloy of Gd with Er, ahomogeneous alloy of Gd with Dy, or a homogeneous alloy of Gd with Ho.26. The process of claim 25, wherein the at least one ortho H₂ to paraH₂ catalyst is ferric oxide.